Discrete Multitone Transmission Research Articles

Unique Word DMT Schemes Using Real-Valued Constellations for IM/DD Optical Systems

Discrete multitone transmission (DMT) schemes employing real-valued constellations such as PAM (PAM-DMT) are popular multi-carrier transmission schemes for optical systems using intensity modulation and direct detection. PAM-DMT employs a data dependent cyclic prefix (CP) to maintain cyclicity. In this letter, we propose a novel DMT scheme using real-valued modulation formats where the usual CPs are replaced by a unique word (UW) that is a known deterministic sequence. This is achieved by designing a code generator matrix in the frequency domain that introduces correlation among the data symbols. The proposed PAM UW-DMT scheme shows a superior bit error ratio performance as compared with PAM CP-DMT. Moreover, the UW can be used for other purposes, such as synchronization and channel estimation.

Performance Comparison of 112-Gb/s DMT, Nyquist PAM4, and Partial-Response PAM4 for Future 5G Ethernet-Based Fronthaul Architecture

For a future 5G Ethernet-based fronthaul architecture, 100G trunk lines of a transmission distance up to 10 km standard single mode fiber (SSMF) in combination with cheap grey optics to daisy chain cell site network interfaces are a promising cost- and power-efficient solution. For such a scenario, different intensity modulation and direct detect (IMDD) Formats at a data rate of 112 Gb/s, namely Nyquist four-level pulse amplitude modulation (PAM4), discrete multi-tone Transmission (DMT) and partial-response (PR) PAM4 are experimentally investigated, using a low-cost electro-absorption modulated laser (EML), a 25G driver and current state-of-the-art high Speed 84 GS/s CMOS digital-to-analog converter (DAC) and analog-to-digital converter (ADC) test chips. Each modulation Format is optimized independently for the desired scenario and their digital signal processing (DSP) requirements are investigated. The performance of Nyquist PAM4 and PR PAM4 depend very much on the efficiency of pre- and post-equalization. We show the necessity for at least 11 FFE-taps for pre-emphasis and up to 41 FFE coefficients at the receiver side. In addition, PR PAM4 requires an MLSE with four states to decode the signal back to a PAM4 signal. On the contrary, bit- and power-loading (BL, PL) is crucial for DMT and an FFT length of at least 512 is necessary. With optimized parameters, all Modulation formats result in a very similar performances, demonstrating a transmission distance of up to 10 km over SSMF with bit error rates (BERs) below a FEC threshold of 4.4E-3, allowing error free transmission.

Nonlinearity-aware 200 Gbit/s DMT transmission for C-band short-reach optical interconnects with a single packaged electro-absorption modulated laser.

We experimentally demonstrate the transmission of a 200Gbit/s discrete multitone (DMT) at the soft forward error correction limit in an intensity-modulation direct-detection system with a single C-band packaged distributed feedback laser and traveling-wave electro absorption modulator (DFB-TWEAM), digital-to-analog converter and photodiode. The bit-power loaded DMT signal is transmitted over 1.6km standard single-mode fiber with a net rate of 166.7Gbit/s, achieving an effective electrical spectrum efficiency of 4.93bit/s/Hz. Meanwhile, net rates of 174.2Gbit/s and 179.5Gbit/s are also demonstrated over 0.8km SSMF and in an optical back-to-back case, respectively. The feature of the packaged DFB-TWEAM is presented. The nonlinearity-aware digital signal processing algorithm for channel equalization is mathematically described, which improves the signal-to-noise ratio up to 3.5dB.

Highly Spectrally Efficient Discrete Multi-Tone Transmission over Step Index PMMA optical fibre for Short-Range Optical Communication

In this article we present high spectral efficiency DMT transmissions over 20 m of Step-Index polymethyl methacrylate optical fiber in the visible range. We demonstrated that using illumination light emitting diodes at 450, 520, 560 and 650 nm it is possible to achieve as high as 6.39 bits/s/Hz for a pre- Forward Error Correction with a target Bit Error Rate of 10-3. The optical source at 560 nm was developed in our laboratory and then we demonstrated its usage as a new channel in WDM system.

High-Speed DMT and VCSEL-Based MMF Transmission Using Pre-Distortion

We present high-speed single-channel discrete multitone (DMT) operations of directly modulated 850-nm vertical-cavity surface-emitting lasers (VCSEL). Successful transmission of 135 Gb/s over 10 m of OM4 multi-mode fiber (MMF) and 114 Gb/s over 550 m is demonstrated below the 7 % overhead hard-decision forward error correction (FEC) bit error rate (BER) limit. At higher BER limits, i.e. 20 % overhead soft-decision FEC, which are of arising interest for these high-speed short-range links, data rates of up to 161 Gb/s are presented. This is enabled by high-bandwidth low-noise VCSEL, which operate in quasi-single mode to overcome the mode dispersion limitations of the MMF. The applied modulation format is DMT in combination with a Volterra-filter-based pre-distortion approach, which pre-compensates the linear and nonlinear behavior of the transmission system, primarily the digital-analog converter, the VCSEL, the MMF, and the photoreceiver. Furthermore, a detailed investigation of the pre-distortion is given by experimental means, showing that the optimum amount of pre-distortion depends on the applied components and the signal bandwidth. This makes it challenging to predict the optimum; however, a pure electrical pre-distortion offers already a fair gain in performance.

Application of OFDM in Diffusion-Based Molecular Communication

In this letter, the application of orthogonal frequency division multiplexing (OFDM) in the area of diffusion-based molecular communication is studied. The focus is on direct current biased optical OFDM, asymmetrically clipped optical OFDM, and pulse amplitude modulation discrete multi-tone transmission known from optical communications. Simulation results show that the OFDM parameters have to be chosen carefully and that the bit error rate performance is in-between that of standard on-off keying transmission with maximum-likelihood sequence estimation and fixed threshold detection. In addition, it is demonstrated that a proposed bit-loading algorithm can further improve the OFDM performance.

3 × 104 Gb/s Single-λ Interconnect of Mode-Division Multiplexed Network With a Multicore Fiber

In this paper, we study the use of silicon microring modulators in an integrated mode-division multiplexing (MDM) network for short-reach interconnects using discrete multitone (DMT) modulation. A fiber grating coupler array is used as a high-speed optical interface between the on-chip mode channels and off-chip multicore fiber (MCF). The whole link has a crosstalk level lower than –23.1 dB. The MDM network can work without the crosstalk compensation of digital signal processing. We present experimental results of the linearity of the silicon microring modulator in terms of spurious-free dynamic range (SFDR). The third-order intermodulation distortion SFDR is 93.4 dB/Hz 2/3 at 20 GHz. We can improve system performance by using adaptive nonlinear equalizer at the DMT receiver to mitigate transmitter and transmission impairments. An aggregate bitrate above 312 Gb/s is achieved with a bit error ratio of 3.8 × 10−3. With the addition of nonlinear equalizer, the line rates of the MDM network can be further increased to about 330 Gb/s. The experimental results demonstrate the feasibility of single wavelength DMT transmission in MDM network with MCF.

Unique Word DMT Schemes for Optical Systems With Intensity Modulation and Direct Detection

Discrete multitone transmission (DMT) schemes, such as asymmetrically clipped DMT and DC-biased DMT, are popular multicarrier transmission schemes for dispersive optical channels employing intensity modulation and direct detection. These transmission schemes utilize a cyclic prefix (CP) to have a simple frequency domain equalization at the receiver. In this paper, we propose two novel DMT signaling schemes for such optical systems, where the guard interval is built of a unique word (UW), i.e., a deterministic data-independent sequence. This approach becomes possible since redundancy is added in the frequency domain and the UW is a part of the discrete Fourier transform interval. The results show that the proposed UW-DMT schemes outperform the conventional CP-DMT schemes in dispersive optical channels. Furthermore, the UW can be additionally used for other purposes, such as synchronization and channel estimation.

PN-PAM scheme for short range optical transmission over SI-POF \u2014 an alternative to Discrete Multi-Tone (DMT) scheme

BackgroundHow to deal with the time-dispersive channel is the main challenge faced by the short-range optical communication systems. In this work a novel pseudo-noise sequence (PN) assisted pulse-amplitude modulated (PN-PAM) transmission scheme for short-range optical communication systems is proposed in this work. With the help of the PN based channel estimation, minimum-phase pre-filter and reduced-state sequence estimation based equalizer, the proposed PAM transmission scheme can significantly reduce the training overhead for channel estimation in the classical PAM systems using decision feedback equalizer (DFE). In addition, the proposed PAM transmission scheme can effectively avoid the error propagation phenomenon in the classical DFE.ResultsTheoretical study shows that the proposed PAM scheme can achieve a 1.5 dB SNR gain with PAM-8 modulation over 50 m step-index polymer optical fiber (SI-POF) channel at a desired BER level of 1×10−3 and 1.2 Gbps transmission rate. Furthermore the hardware experiment using commercially available components proves the improvements in the proposed PAM transmission scheme.ConclusionThe novel PAM transmission scheme is compared to the optimized discrete multi-tone (DMT) transmission with bit-loading. The experimental results show that for a transmission distance less than 50 m over SI-POF, DMT systems outperform the PAM systems. However, for a SI-POF transmission over the distance longer than 50 m, the proposed scheme can reach a better performance than the DMT systems thanks to the advantage of a lower peak-to-average-power ratio.

26-Gb/s DMT Transmission Using Full $C$ -Band Tunable VCSEL for Converged PONs

Wavelength division multiplex (WDM) passive optical network (PON) is considered for converged fixed mobile broadband access networking. We propose to utilize low-cost tunable lasers at the remote sites, together with a centralized wavelength locker. Practical implementations require a transparently added downstream signaling channel and upstream per-channel pilot tones for channel tagging and remote wavelength control. We demonstrate, for the first time, 26-Gbps discrete multitone transmission modulated on a low-cost wide tunable vertical surface emitting laser over up to 40 km of standard single-mode fiber. The results confirm that converged fixed mobile WDM-PON systems based on low-cost lasers carrying discrete multitone modulation are a technically viable approach.

Demonstration of 4 lanes of 4 × 100 Gbps DMT transmission with channel spacing of 50-GHz compatible with DWDM

Abstract We experimentally demonstrate 4 lanes of 416-Gb/s discrete multi-tone (DMT) transmission with 50-GHz channel spacing. This is the first demonstration of 4 × 100 G transmission with less than 100-GHz channel spacing and it can be compatible with dense wavelength division multiplexing (DWDM).

Demonstration of 4 × 100 Gbps discrete multitone transmission using electric absorption modulated laser at 1550-nm for dense wavelength division multiplexing intradata center connect

We experimentally demonstrate 4 lanes up to 400 Gbps discrete multitone transmission using an electric absorption modulated laser (EML) at 1550-nm for dense wavelength division multiplexing (DWDM) intradata center connects. This is the first demonstration of 4×100 Gb/s transmission using EML at 1550-nm, and it is compatible with the DWDM system at C-band.

Discrete Multitone Transmission at Net Data Rate of 250 ${\text{Gb/s}}$ Using Digital-Preprocessed Analog-Multiplexed DAC With Halved Clock Frequency and Suppressed Image

We demonstrate the first single-lane intensity-modulated direct-detection (IMDD) optical transmission at a net data rate of 250 Gb/s. A discrete multi-tone (DMT) signal at a gross line rate of 300 Gb/s can be generated with a digital-preprocessed analog-multiplexed digital-to-analog converter (DP-AM-DAC), which consists of a digital preprocessor, two sub-DACs, and an analog multiplexer (AMUX). We show a new scheme to relax the required clock frequency to drive the AMUX in the DP-AM-DAC by half to make it easier to extend the bandwidth of the final output signal. The image signal in the final output is also suppressed by the new scheme. In the experiment, we drove the AMUX at 37.5 GHz to generate the DMT signal with a bandwidth of 61.5 GHz. As the optical transmitter, we used an O-band externally modulated laser with a 3-dB electrooptic bandwidth of >55 GHz. After transmission over a 10-km single-mode fiber with an optical fiber amplifier, the signal was received with a bit error rate below the threshold of 20%-overhead soft-decision forward error correction code.

Discrete Multi-Tone Digital Subscriber Loop Performance in the Face of Impulsive Noise

As an important solution to “the last mile” access, digital subscriber loops (DSLs) are still maintained in a huge plant to support low-cost but high-quality broadband network access through telephone lines. The discrete multi-tone (DMT) transmissions constitute a baseband version of the ubiquitous orthogonal frequency division multiplexing. While the DMT is ideally suited to deal with the frequency selective channel in DSL, the presence of bursty impulsive noise tends to severely degrade the transmission performance. In this paper, we analyze the statistics of impulsive noise and its effects on the received signals, with the aid of a hidden semi-Markov process. The closed-form bit error rate expression is derived for the DMT system for $Q$ -ary quadrature amplitude modulation under practical noise conditions and for measured dispersive DSL channels. Instead of relying on the simplified stationary and impulsive noise process, our noise model considers both the temporal and spectral characteristics based on the measurement results. The simulation results confirm the accuracy of the formulas derived and quantify the impact both of the impulsive noise and of the dispersive channel in DSL.

IQ imbalance tolerable parallel-channel DMT transmission for coherent optical OFDMA access network

Abstract Phase diversity of coherent optical communication provides spectrally efficient higher-order modulation for optical communications. However, in-phase/quadrature (IQ) imbalance in coherent optical communication degrades transmission performance by introducing unwanted signal distortions. In a coherent optical orthogonal frequency division multiple access (OFDMA) passive optical network (PON), IQ imbalance-induced signal distortions degrade transmission performance by interferences of mirror subcarriers, inter-symbol interference (ISI), and inter-channel interference (ICI). We propose parallel-channel discrete multitone (DMT) transmission to mitigate transceiver IQ imbalance-induced signal distortions in coherent orthogonal frequency division multiplexing (OFDM) transmissions. We experimentally demonstrate the effectiveness of parallel-channel DMT transmission compared with that of OFDM transmission in the presence of IQ imbalance.

Self-reverse-biased solar panel optical receiver for simultaneous visible light communication and energy harvesting.

We propose a self-reverse-biased solar panel optical receiver for energy harvesting and visible light communication. Since the solar panel converts an optical component into an electrical component, it provides both energy harvesting and communication. The signal component can be separated from the direct current component, and these components are used for communication and energy harvesting. We employed a self-reverse-biased receiver circuit to improve the communication and energy harvesting performance. The reverse bias on the solar panel improves the responsivity and response time. The proposed system achieved 17.05 mbps discrete multitone transmission with a bit error rate of 1.1 x 10-3 and enhanced solar energy conversion efficiency.

Performance study of DMT transmission for next generation passive optical network

Discrete multi-tone (DMT) based passive optical network (PON) is a subject of great interest for recent research works, due to its high spectral efficiency, high flexibility and high tolerance to the fiber chromatic dispersion. In this paper, we investigate the transmission performance of DMT transmission for next generation PON, including the optimization of modulation index and the power fading of double sideband (DSB) induced by chromatic dispersion. A new single sideband (SSB) DMT modulation based on a dual-driver Mach-Zehnder modulator (DDMZM) is also presented, which can eliminate the power fading. The simulation results show that 4×25Gb/s DSB DMT-PON combining with wavelength division multiplexing (WDM) and the single wavelength 100Gb/s SSB-DMT are both promising candidates for future access network.

Discrete Multi-Tone Transmission With Optimized QAM Constellations for Short-Reach Optical Communications

We investigate performance of optimized M-ary quadrature amplitude modulation (M-QAM) constellations in short-reach single-polarization (SP) and dual-polarization (DP) discrete multitone (DMT) with direct detection. The constellations are obtained by using an iterative gradient-search algorithm. For the nonsquare constellations, we find bit-to-symbol mappings with a blind search method. Our experiments show that the data rate can be improved in both SP and DP DMT systems by using optimized constellations instead of square M-QAM. Net data transmission rates of 165 and 152 Gb/s are respectively achieved for back-to-back and 2.2 km in a direct-detection DP DMT system assuming forward error correction threshold of $3.8\times 10^{-3}$ .

Solutions for 80 km DWDM Systems

Currently discussed solutions for 80 km DWDM transmission targeting inter-data center connections at 100G and 400G line rates are reviewed. PDM-64QAM, PAM4, and discrete multi-tone transmission (DMT) are investigated, while the focus lies on directly detected solutions. For DMT, the vestigial sideband approach significantly increases the tolerance toward chromatic dispersion and bandwidth limitation and gives way to a flexible DWDM 400G transceiver using four to eight wavelengths.

Silicon IQ Modulator for Next-Generation Metro Network

Silicon photonics have been extensively demonstrated as the promising solution for low-cost and high-performance transmission network. We show that silicon Mach–Zehnder IQ modulators are capable for next-generation metro network applications. The transmission distances cover whole metro transmission range, up to 960 km. We experimentally demonstrated different modulation formats for different scenarios with these modulators. For 320-km transmission, 56 Gb/s single-sideband discrete multitone transmission was achieved. For 480 km, 80 × 453.2-Gb/s polarization division multiplexing (PDM) orthogonal frequency-division multiplexing hybrid 8–64 quadrature amplitude modulation (QAM) dense wavelength division multiplexing signals transmission was achieved. Finally, 80 × 337.9-Gb/s transmission of Nyquist-WDM PDM-16QAM was achieved for 960 km.